Aromatic chemistry and amines

Explain why modern benzene is more thermodynamically stable than kekule structure 

Electrons delocalised in a ring,overlap of p orbital 

Name the mechanism + reagents +conditions for the reaction of sulfuric+nitric acid with benzene

Electrophillic addition 

Concentrated H2SO4 and HNO3

Reflux 

Explain the bonding in benzene

Each c has 3 covalent bonds

Spare electrons in p orbital overlap to form a pie cloud 

Delocalisation 

Explain the shape of benzene 

Planar 

Hexagon /6 C ring 

C-C bonds equal in length 

Compare the stability of benzene with that of hypothetical cyclohexa 1,3,5 triene

Enthalpy of hydrogenation of cyclohexene is =-360

Enthalpy of hydrogenation of benzene less exothermic by 152kj mol

Benzene Lower in energy so more stable

Because of delocalisation 

Suggest a value for Enthalpy of hydrogenation of cyclohexa 1,3 diene

Justify 

-239 to -121

Double bonds separated by one single bond

Allows some delocalisation of p orbitals 

Use Enthalpy of hydrogenation data to show that benzene is 152kj mol more stable than hypothetical compound of cyclohexa-1,3,5-triene

3(-120)-(-208)=-152

State in terms of bonding why benzene is more stable than kekule (1)

Benzene ring of delocalised electrons

Suggest bond lengths for

Single bond in kekule 

Double bond in kekule 

Single bond in benzene 

147

135

140

Give the 2 equations for the formation of a nitronium ion

H2so4 + HNO3——> HSO4 minus + H2NO3 plus

H2NO3 plus ——→ NO2 plus + H20

Give the overall equation for the formation of nitronium ion

H2so4 + HNO3—→HSO4- + NO2+ +H20

What are the two types of electrophillic substitution and conditions for each?

Nitration-conc h2so4 and Hno3, warm-UNDER 55 degrees for single

Friedel craft acylation

Acyl chloride

Alcl3 catalyst

Reflux

dry ether

What is the electrophille in acylation and what does this form as products

Acylium ion

Phenyl ketone and HCL

What do you use to prepare aromatic amines

Equation for nitrobenzene

using tin/sn and HCL

Reducing agent

C6H5NO2+ 6H —→ C6H5NH2+ 2H20

Why aq solution obtained in reduction of nitrobenzene even tho phenylamine insoluble

C6H5NH2 ionic salt

Give two step synthesis of aliphatic amine

And give strengths weaknesses

Nucleophillic sub aq ethanolic KCN

Reduction of nitrile H2 Nickel

-high atom economy

-single product/pure

-low% yielf

Give one step synthesis of aliphatic amine

Strengths and weaknesses

NH3 excess nucleophillic substitution

Low atom economy

Further substitution-impure product

How can you ensure major product is quaternary salt

Excess haloalkane

Suggest why amines with benzene ring are weaker 

Lone pair on N 

Delocalised into the ring 

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